The synthesis of the inducible liver protein, metallothionein, is being studied after and during the induction by various metals, such as zinc, cadmium, copper, and mercury. The various techniques being used include in vivo and ex vivo studies with rat liver. The latter is being done with the use of the isolated perfused liver method (MRA Corp.). Liver perfusion and the successful induction of metallothionein has been carried out on the platform for up to four hours. Synthesis of metallothionein has been demonstrated using tracers, both amino acids and metals, and inhibitors, actinomycin D, cycloheximide, and cordycepin. Sephadex G-75 column chromatography and atomic absorption spectroscopy have been used to quantitate the amount of metallothionein in liver on a routine basis. More recently, a radioimmunoassay has been developed to measure more sensitively the amount of metallothionein. Currently, attempts are being made to develop an isolated kidney system to ascertain the ability of this organ to synthesize metallothionein.